The present invention relates to a head positioning device used for a memory system, for use in a computer, such as a magnetic disc type memory system utilizing a disc as a recording medium and having a read/write head movable to a position.
As the devices of this kind, there have been known a loop-winding system such that a metallic band is extended between a capstan and an idle roller as shown in FIG. 7, and an .alpha.-winding system as desclosed, for instance, in U.S. Pat. No. 4,161,004 (Japanese Unexamined Patent Publication No. 123911/1978) as shown in FIG. 8.
In these Figures, a reference numeral 1 designates a magnetic disc as a recording medium, a numeral 2 designates a read/write head, a numeral 3 designates a carriage to which a magnetic head 2 is attached, a numeral 4 designates a head driving motor such as a step motor, a numeral 5 designates a capstan attached to the shaft of the motor 4, a numeral 6 designates an idle roller, a numeral 7 designates a metallic band extended between the capstan 5 and the idle roller 6, the metallic band supporting the carriage 3, and a numeral 8 designates a band fixing piece. In FIG. 8, a numeral 9 designates a supporting piece for supporting the metallic band wound around the capstan 5 in a form of a letter of a.
The operation of the conventional devices will be described.
In the both devices, the head driving motor 4 rotates the capstan 5. Since the metallic band 7 wound around the capstan 5 is secured at its part to the capstan 5 by the band fixing piece 8 or spot-welding, the movement of rotation of the capstan 5 gives to the metallic band 7 a linear motion. Accordingly, the carriage 3 attached to the metallic band 7 undergoes the linear movement in accordance with the movement of rotation of the motor 4 so that the carriage is stopped at a desired position. In the loop-winding system as shown in FIG. 7, the idle roller 6 is pulled by a spring to give an appropriate tension to the band 7 so that the quantity of movement of the carriage 3 resulted when the capstan 5 is turned to a direction is not different from the quantity of movement of the carriage 3 resulted when the capstan 5 is turned to the other direction. On the other hand, in the .alpha.-winding system as shown in FIG. 8, the supporting piece 9 is used to secure one end of the band 7 and a plate spring (not shown) is disposed to connect the other end of the band 7, whereby a tension is given to the band 7.
In the conventional loop-winding system as shown in FIG. 7, the angle of rotation of the capstan 5 cannot exceed 180.degree.. Accordingly, when the same pitch of feeding of the carriage as in the .alpha.-winding system capable of rotating the capstan by nearly 360.degree. is to be given, it is necessary to make the diameter of the capstan greater than that used for .alpha.-winding system as shown in FIG. 8 and to use a highly accurate step motor in which an pitch angle is reduced to about half. In the .alpha.-winding system, while the capstan 5 can rotate by nearly 360.degree., it is necessary to provide a space for allowing the supporting piece 9 to move in the opposite direction of the head 2. Accordingly, miniaturization of the device is hindered.